The present invention relates to a coaxial-line section.
A coaxial-line section of the concerned type includes an outer conductor provided with a connecting flange at each end thereof and surrounding an insulator or bead for centering an inner conductor coupling. Each end of the coupling is provided with a supporting ring which is surrounded by a ring of compound springs for contacting an inner conductor and allowing a thermal expansion of the latter.
When transmitting very high RF-powers through coaxial lines consisting of such sections, the coaxial line is considerably heated up whereby the excess temperature of the inner conductor is substantially higher than that of the outer conductor. For example, at a power of 15 MW and an ambient temperature of 40.degree. C., the temperature of an inner conductor of copper may rise to 250.degree. C. or more while the temperature of an outer conductor of aluminum may rise to 110.degree. C. and more, thereby causing considerable thermal expansions. Since the expansion of the inner conductor exceeds the thermal expansion of the outer conductor, the laminated spring rings contacting the inner conductor are dimensioned with sufficient length for compensating the greater expansion of the inner conductor tube without encountering constraining forces even when considering manufacturing tolerances and dimensional tolerances. Taking into account these considerations, a section with a mean length of for example 5 m results in a length for the laminated springs of up to several centimeters. Even when assuming a horizontal laying of the coaxial-line section, the expansion of the inner conductor tube will not be uniform at both its ends so that the cross sectional center plane of the inner conductor tube which defines the center of gravity does not remain stationary. This is even more true upon slanting or vertical laying of the coaxial-line sections.
Consequently, upon laying of the coaxial-line section or during the course of several switching cycles, one end of the inner conductor tube will completely cover the laminated spring while the other laminated spring ring has to compensate all assembling tolerances and the entire thermal expansion. Taking into account that this respective end of the inner conductor tube should not be out of contact from the laminated spring ring even at lowest ambient temperatures, it is evident that these conditions will not guarantee a secure contacting between the inner conductor tube and the respective inner conductor couplings because the available spring deflection in the direction toward the root of the laminated springs decreases while the spring force increases in the direction toward the exposed and the supporting ring facing end of the laminated springs. Especially when transmitting very high RF-powers, an absolute secure contacting is mandatory. However, such known coaxial-line section satisfies this requirement for the above-stated reasons only in the central area of the laminated springs.